The giant elliptical galaxy M60 and the spiral galaxy NGC 4647 make an odd couple Hubble Space Telescope image. They’re found in a region of space where galaxies tend to gather, on the eastern side of the nearby Virgo Galaxy Cluster. About 54 million light-years away, M60’s simple egg-like shape about 120,000 light-years across is created by its randomly swarming older stars. NGC 4647’s young blue stars, gas and dust are an organized spiral, winding arms rotating in a flattened disk spanning 90,000 light-years. It’s about the same size as our galaxy, the Milky Way. NGC 4647 is more distant than M60, around 63 million light-years from Earth. The pair of galaxies which is known as Arp116 may be close enough to be on the verge of a significant gravitational encounter.
Over next couple of billion years, these two spiral galaxies will end up in a complete galactic merger—the two galaxies will become a single, larger one. They’re about 150 million light-years away in the constellation of Canis Major (the Great Dog), so what we can see now is what was happening 150 million years ago.
The gravitational attraction of NGC 2207, the larger of the pair, is already stirring things up throughout its smaller partner, distorting IC 2163’s shape and throwing stars and gas into long streamers that extend over 100,000 light-years. However, most of the space between stars in a galaxy is empty. When these galaxies collide, almost none of the stars in them will crash into another star.
This 150 million old image is a vision of the Milky Way’s future. About the time NGC 2207 and IC 2163 have finished their merger, the Milky Way will begin colliding with the Andromeda Galaxy.
The dense star cluster called R136 is located within the Tarantula Nebula (also known as 30 Doradus), a giant star-forming region in a nearby dwarf galaxy. This computer simulation shows the gravitational interaction of two young star clusters that are believed to have merged to form R136. 3.5 million years of the encounter have been compressed into 27 seconds. After the first interaction, the pair of star clusters become gravitationally entwined and eventually merge together.